1. Field of the Invention
The present invention relates to the field of tube expanders.
2. Background
For heat exchangers and other similar devices, fins are mounted to tubes to provide an efficient means for transferring heat either to or from a medium circulated within the tubes while air or other gas is passed over the fins. Typically, the fins are fitted onto the tubes and subsequently expanded to create a secure mechanical bond between the fins and the tubes. It is desirable to expand the tubes to a larger outside diameter than the inside diameter of the fin holes receiving the tubes to produce a very tight mechanical bond between the fins and the tubes. A known tube expander for achieving such an outer diameter expansion of the tubes is disclosed in U.S. Pat. No. 3,789,648 to Ames. The tube expander of U.S. Pat. No. 3,789,648 includes a pair of oppositely turning rod driver gears coupled by gears to a hydraulic motor to longitudinally drive a rounded end of the rod into and out of the tubes. The driving of the rod by the wheels is achieved by a friction and/or pressure fit of a smooth outer diameter surface of each rod driver gear in contact with a periphery of the rod. A problem associated with a friction and/or pressure fit is the wear and tear on the rod by the rod driver gears that can significantly reduce the useable life of the rod. Another problem associated with a friction and/or pressure fit is the rod must be significantly hardened to minimize the potentiality of the rod breaking as the rod driver gears are driving the rounded end of the rod into and out of the tubes.
It is also known to positively drive the expander rod by forming a rack on the top surface thereof and a rack on the bottom surface thereof, and then drivingly engaging the rack teeth with a pair of oppositely driven pinion gears placed adjacent the top rack and the bottom rack. A typical rack and pinion arrangement is shown in U.S. Pat. No. 5,673,665.